A variety of techniques and instruments have been developed for use in the removal or repair of tissue in arteries and similar body passageways. A frequent objective of such techniques and instruments is the removal of atherosclerotic plaque in a patient's arteries. Atherosclerosis is characterized by the buildup of fatty deposits (atheromas) in the intimal layer (i.e., under the endothelium) of a patient's blood vessels. Very often over time what initially is deposited as relatively soft, cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque. Such atheromas restrict the flow of blood, and therefore often are referred to as stenotic lesions or stenoses, the blocking material being referred to as stenotic material. If left untreated, such stenoses can cause angina, hypertension, myocardial infarction, strokes and the like.
Several kinds of atherectomy devices have been developed for attempting to remove some or all of such stenotic material. In one type of device, such as that shown in U.S. Pat. No. 4,990,134 (Auth), a rotating burr covered with an abrasive cutting material, such as diamond grit (diamond particles or dust), is carried at the distal end of a flexible, rotatable drive shaft.
U.S. Pat. No. 5,314,438 (Shturman, the teachings of which are incorporated herein by reference) shows another atherectomy device having a rotatable drive shaft with a section of the drive shaft having an enlarged diameter, at least a segment of this enlarged diameter section being covered with an abrasive material to define an abrasive segment of the drive shaft. When rotated at high speeds, the abrasive segment is capable of removing stenotic tissue from an artery.
U.S. Pat. No. 5,314,407 (Auth, the teachings of which are incorporated herein by reference) shows details of a type of handle which may be used in conjunction with rotational atherectomy devices of the type shown in the Auth '134 and Shturman '438 patents. A handle of the type shown in the Auth '407 patent has been commercialized by Heart Technology, Inc. (Redmond, Wash.), now owned by Boston Scientific Corporation (Natick, Mass.) in the rotational atherectomy device sold under the trademark Rotablator.RTM..
FIG. 1 schematically illustrates a Rotablator.RTM. atherectomy device. This atherectomy device generally includes an elongate, generally tubular handle A which slidably carries a prime mover carriage B. A compressed gas driven turbine (not shown) is carried by the prime mover carriage B. The turbine is connected to a drive shaft C having an abrasive-coated burr D at its distal end. The drive shaft and the burr are rotated at high speeds, typically in the range of about 140,000 to about 180,000 rpm. The drive shaft C is designed to be advanced over and rotated around a guide wire E, which is typically held in place using a pneumatic guide wire clamp (not shown) in the proximal end portion of the handle A. Most of the length of the drive shaft is disposed inside a catheter F.
The rotational speed of the compressed gas turbine of the Rotablator.RTM. device is determined by a fiber optic tachometer. This tachometer includes a fiber optic cable assembly G which is attached to the prime mover carriage B via a rigid dual fiber optic connector H. The fiber optic cable assembly G comprises two separate fiber optic cables--a first fiber optic cable I which carries light from a light source into the prime mover carriage B, and a second fiber optic cable J which carries light from the prime mover carriage back to a light detector. A proximal end portion of each of these fiber optic cables I and J is rigidly mounted in the dual fiber optic connector H. A distal end portion of each of these fiber optic cables is provided with a standard Hewlett-Packard type click-fit plug K to permit the first fiber optic cable I to be snap-fit into a light emitting diode module and the second fiber optic cable J to be snap-fit into a photodetector module.
FIGS. 2 and 3 are schematic cross sectional views through the Rotablator.RTM. device taken along line 2--2 of FIG. 1. As shown in these drawings, the dual fiber optic connector H comprises a metal fitting L which fixes the relative positions of the proximal end portions of the fiber optic cables I and J. A portion of a plastic jacket M is retained within the distal portion of the metal fitting L. As best seen in FIG. 3A, an outer crimping ring Q is used to secure the proximal end portions of the fiber optic cables I and J within the metal fitting L. The plastic jacket M is common to both of the fiber optic cables I and J. The metal fitting is rigidly secured within the prime mover carriage B to hold the ends of the two fiber optic cables I and J at a precise location within the prime mover carriage B.
The fiber optic tachometer of the Rotablator.RTM. device also includes a tachometer rotor N mounted on a shaft P of the prime mover. The rotor N has an exterior surface which is substantially non-reflective. The rotor also includes two generally hemispherical reflective surfaces O located on diametrically opposite sides of the rotor. As the rotor N rotates together with the prime mover shaft P within the prime mover carriage B, the rotor will move from a position wherein one of the reflective surfaces O is positioned adjacent the proximal ends of the fiber optic cables I and J (FIG. 2) to a position wherein the non-reflective exterior surface of the rotor is positioned adjacent the proximal ends of the fiber optic cables I and J (FIG. 3).